The present invention relates to a transmit phase control system of synchronization burst (hereinafter abbreviated as "sync burst") and, more particularly, to a sync burst transmit phase control system for establishing and maintaining a TDMA (Time Division Multiple Access) frame between a plurality of earth stations which are capable of communicating with each other via a communications "satellite based on an SS/TDMA (Satellite-Switched Time Division Multiple Access") system.
An SS/TDMA system, among others, is a promissing implementation for satellite communications which allows a plurality of earth stations to hold communications by way of a large capacity satellite. The SS/TDMA system is constituted by a communications satellite which is provided with a switch matrix, a switch matrix controller and a plurality of spot antennas, and a plurality of earth stations. Each of the spot antennas emits a spot beam for irradiating a limited beam spot zone on the surface of the earth, and receives an electromagnetic wave which is radiated from an earth station located in a beam spot area. The switch matrix controller controls the switching of the switch matrix to allow any earth stations to hold a communication between themselves. Since the switching of the switch matrix is performed on the basis of a timing reference which is generated by the switch matrix controller of the satellite, each earth station has to synchronize its own timing reference to the satellite onboard timing reference. The transmit phase control of a sync burst is adapted to implement such synchronization. A method of controlling sync burst transmit phase is disclosed in, for example, European Patent Application No. A.sub.2 0 152 108 laid open for public inspection on Aug. 21, 1985. A problem with the method disclosed in this European application is that a metric pattern included in a sync burst is selected unalterably. The metric pattern is not always optimum, depending upon the adjustment of a demodulator which is built in the earth station. A result is the lowering of the accuracy of the transmit phase control.